Organothallium-nitrogen compounds

Complex supramolecular architectures have been established for dimethyl-thallium(III) derivatives of polyfunctional nitrogen ligands, e.g. the cyanide, the azide, the cyanate, the thiocyanate [177], the dicyanamide, and the tricyanomethide [178], The cyanide, Me2TlCN, 53, contains layers of nearly coplanar CN groups 

The structure of the trigonal cyanate warrants special comment. It is different 

In the dicyanamide, 57, and the tricyanomethide, 58, dimethylthallium(lll) derivatives the structure of the ligands determines the formation of large rings, as part of complex supramolecular architectures. 

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The recently reported (757) conversion of 5-pyrazolones directly to a,j8-acetylenic esters by treatment with TTN in methanol appears to be an example of thallation of a heterocyclic enamine the suggested mechanism involves initial electrophilic thallation of the 3-pyrazolin-5-one tautomer of the 5-pyrazolone to give an intermediate organothallium compound which undergoes a subsequent oxidation by a second equivalent of TTN to give a diazacyclopentadienone. Solvolysis by methanol, with concomitant elimination of nitrogen and thallium(I), yields the a,)S-acetylenic ester in excellent (78-95%) yield (Scheme 35). Since 5-pyrazolones may be prepared in quantitative yield by the reaction of /3-keto esters with hydrazine (168), this conversion represents in a formal sense the dehydration of /3-keto esters. In fact, the direct conversion of /3-keto esters to a,jS-acetylenic esters without isolation of the intermediate 5-pyrazolones can be achieved by treatment in methanol solution first with hydrazine and then with TTN. 

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